The present invention is suitable for use especially in cellular radio systems and also in other digital radio systems where terminal equipments communicating with base stations move beyond cell boundaries. Information on the moving speed of the terminal equipment will make it essentially easier to manage resources of the radio system, such as handover anticipation and power control optimization.
For example, in a system using small microcells and bigger, so-called umbrella cells overlapping microcells, it is advantageous that fast moving terminal equipments are connected to umbrella cells and slowly moving or stationary terminal equipments to smaller microcells. In this way it is possible to diminish significantly the number of required handovers and thus signalling loading in the network.
One known solution for determining the speed of a mobile terminal equipment is to monitor Doppler shift of carrier frequency. This method is, however, impractical as it requires a stable frequency reference source which is expensive.
Another known method has been described in Doumi T., Gardiner J. G., Use of base station diversity for mobile speed estimation, Electronic Letters, Vol. 30, No. 22, pp. 1835-1836. The method of the reference cited utilizes base station antenna diversity. The antenna providing the strongest signal level is always selected for diversity. The frequency shift of the antenna is proportional to Doppler shift on the basis of which the speed of the equipment can be deduced.
U.S. Pat. No. 5,396,645 describes a method for measuring the speed of an equipment. In the method of the reference cited, variations of the strength of a received signal are measured during a predetermined time interval and the speed of the equipment is deduced on the basis of this variation.
None of the known methods is, however, suitable in a TDMA radio system where frequency hopping is used, that is, where the carrier frequency used by the user of the equipments varies by time slots in accordance with some given variance pattern.